tan (n.)

"bronze color imparted to skin by exposure to sun," 1749, see tan (v.). Earlier as "substance made of crushed bark used in making leather" (c. 1600). As a simple name for a brownish color, in any context, it is recorded from 1888. The adjective meaning "of the color of tanned leather" is recorded from 1660s. Tan-line attested from 1979.

tan (v.)

late Old English tannian "to convert hide into leather" (by steeping it in tannin), from Medieval Latin tannare "tan, dye a tawny color" (c.900), from tannum "crushed oak bark," used in tanning leather, probably from a Celtic source (such as Breton tann "oak tree"). The meaning "make brown by exposure to the sun" (as tanning does to hides) first recorded 1520s; intransitive sense also from 1520s. Of persons, not considered an attractive feature until 20c.; in Shakespeare, "to deprive of the freshness and beauty of youth" (Sonnet CXV). As an adjective from 1620s. To tan (someone's) hide in the figurative sense is from 1660s. Related: Tanned; tanning. German Tanne "fir tree" (as in Tannenbaum) might be a transferred meaning from the same Celtic source.